Any semiconductor die that produces a large amount of heat, such as a power semiconductor die, a data processor die, a memory die, etc., is limited by the rate at which heat can be dissipated from it.
When a die processes more power and/or data, the die produces more heat. To keep the temperature of a die under the failure value, heat has to be dissipated from the die at the fastest possible rate. Therefore, the density of power and/or data processing is limited by the rate at which heat can be dissipated from these dies. Conversely, more power and/or data can be processed by a die if the rate of heat dissipation from the die can be increased.
The amount of power and/or data that a die processes is limited by the amount of heat that can be dissipated from the die using the conventional heat-dissipation techniques. One known technique for dissipating heat from a power semiconductor is to bond the semiconductor die to a thermally-conductive, electrically-insulative substrate, such as a ceramic substrate. The ceramic layer is typically mounted on a metallic substrate, which may be mounted on an actively cooled device, such as a cold plate. Heat from the semiconductor is transferred to the ceramic substrate and then to the cold plate. One limitation of this known technique for dissipating heat is that heat is only removed from one side of the semiconductor, i.e., the side bonded to the thermally-conductive, electrically-insulative substrate.
The bonding of the semiconductor die to the thermally-conductive, electrically-insulative substrate may cause heat-related problems. Unless the thermally-conductive, electrically-insulative substrate and the semiconductor die are made of materials with identical expansion coefficients, the heat generated in the semiconductor device will cause the substrate and the semiconductor die to expand at differing amounts and at differing rates. This differing expansion may cause physical stresses that may eventually damage the semiconductor assembly.
Another heat and bonding related problem may result where the electrical leads, such as the gate and source wires, are connected to the semiconductor die. The leads and the die are typically connected using an inelastic bonding method, such as welding. The electrical leads are typically thin wires that are vibration welded to the metallized surface of the semiconductor die. Because the lead wires are thin, the area where the lead wires are welded to the semiconductor die (i.e., the bonding point) is small. As a large amount of current would typically flow through the small bonding point (this may be termed current crowding at a singularity point), the temperature excursion that occurs at the bonding point is greater than the temperature excursion that occurs in the other areas of the semiconductor die. As a result, greater expansion occurs at the bonding point, increasing the physical stress and increasing the likelihood of failure of the weld, the lead, and/or the die.
As such, there is a need for a semiconductor device and cooling apparatus that enables greater heat dissipation to enable increased power/data flow and which eliminates inelastic bonding to thereby decrease the likelihood of failure due to physical stress caused by the expansion of dissimilar materials.